Merge commit '29cc80f4ecaf' from llvm.org/main into next

Author: git apple-llvm automerger

libcxx/include/__memory/construct_at.h

@@ -44,7 +44,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr _Tp* construct_at(_Tp* __location, _Args&&... __
 #endif
 
 template <class _Tp, class... _Args, class = decltype(::new(std::declval<void*>()) _Tp(std::declval<_Args>()...))>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Tp* __construct_at(_Tp* __location, _Args&&... __args) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* __construct_at(_Tp* __location, _Args&&... __args) {
 #if _LIBCPP_STD_VER >= 20
   return std::construct_at(__location, std::forward<_Args>(__args)...);
 #else